1. Field of the Invention
The invention is directed to an automatic product feed for a milling roller mill having a mechanical sensor, a product feed device with adjustable drive means for the feed rolls, as well as engaging and disengaging means for the grinding rolls, and to a method for controlling the grinding in a milling roller mill.
2. Description of the Related Art
Strictly defined general conditions must be met for regulating the product feed in a milling roller mill. They are:
a uniform product distribution over the entire length of the grinding rolls PA0 the amount of product flowing into the roller mill must be processed within a bandwidth and metered to the grinding rolls while compensating for temporary feed fluctuations as far as possible; PA0 during an interruption in the product feed to the roller mill, the product feed to the grinding rolls must be stopped with minimum delay and the grinding rolls must be moved apart simultaneously. PA0 a mechanical arrangement is still the most inexpensive of all sensor technologies. PA0 a mechanical arrangement is more reliable and requires no specialized technical background for handling. PA0 a mechanical arrangement always has frictional forces in every movement. PA0 the regulation of the amount of product PA0 engagement and disengagement, PA0 An optimal feed roll speed can be adjusted, depending on grinding conditions, in the regulation of the amount of product by regulating the segment approximately in accordance with EP-PS 38 054 via a pneumatic regulation of the metering gap. PA0 An optimal value can be adjusted for the metering gap by means of a digital signal of a control unit in regulating the product amount by means of regulating the feed roll speed according to DE-GM 86 14 505.
With respect to apparatus, various basic elements such as distributing rolls and feed rolls as well as a mechanical probe as sensor for precision regulation of the flow to the grinding rolls have been used successfully for decades. In principle, the momentary adjustment of the amount of product flowing into the grinding rolls can be effected in two ways: by regulating the rate of rotation or speed of the feed rolls or by regulating the metering gap between a proportioning slide and the feed roll which is also known as segment distribution.
Both arrangements, i.e. speed regulation and segment distribution, are currently practiced.
An example of speed regulation is described in DE-GM No. 86 14 505 and has proven very successful for some applications. However, speed regulation is not as widely used as segment distribution. A regulation of the metering gap is disclosed in EP-PS 38 054, likewise by the present Applicant. When the product to be metered has a flour-like or gritty quality, segment distribution is preferred in practice by the majority of millers. On the other hand, speed regulation has often proved superior to segment distribution in the case of flaky products as in the metering of break, e.g. prior to the second grinding passage in the mill.
The problem which now arises consists in the fact that it must first be determined in principle for every roller mill which concept to install for regulating the feed. A subsequent conversion is often not carried out and thus an absence of optimal feed regulation may recur repeatedly in individual grinding passages.
The grinding process is acknowledged as the core of every mill. Therefore, the quality of the grinding is influenced by a number of parameters. Special importance is attached to the regulation of the product feed to the grinding rolls and to trouble-free operation of the elements required for this. The degree of automation in a modern mill has already reached a particularly high level. A further increase in automation is demanded, not least of all, to ensure quality, at least to the extent that the parameters already presently influenced by hardware technology can be exploited to achieve even greater perfection so as to enable easier access through human intervention and management of the process.
Significantly, an actual conflict of goals can be discerned precisely in regard to the roller mill. This is caused in part by prejudices of an almost ideological character, even in technical circles. Some say that mechanics are now out of date, that modern techniques such as electronics or sensor technology, e.g. optical, capacitive, infrared measuring technology, are superior and more advantageous since electrical/electronic signals are generated immediately. Many trained specialists still attach an almost mystical significance to computer technology accompanied by a strong reliance or euphoric acceptance. As a result, a great number of solutions are offered, each of which, without exception, has achieved only partial acceptance.